Nuclear fuel as radioactive waste is stored in a storage canister in a nuclear facility of a nuclear power plant and so on. The nuclear fuel is transported from the storage canister to a nuclear waste storage facility 100 in FIG. 1 so as to be stored for an extended period. In the storage facility 100, a cask 101 contains a storage canister 102. There is a concern that the metallic storage canister 102 may have stress corrosion cracking. The storage canister 102 may have stress corrosion cracking if a tensile stress remains on an austenitic stainless steel material constituting the storage canister 102 in a corrosive environment of sea salt or the like. As shown in FIG. 1, vent holes 101a and 101b are formed at the top and bottom of the cask 101 so as to dissipate heat, which is generated by the nuclear fuel, from the surface of the storage canister 102. Since the outside air is passed through the vent holes 101a and 101b, the storage canister 102 is kept exposed to the outside air. In Japan, the nuclear waste storage facility 100 is built in a coastal region and thus cannot avoid a corrosive environment of sea salt and so on.
A tensile stress remaining on the storage canister 102 is a tensile residual stress that occurs when a cover is welded to a body constituting the storage canister 102. In a known technique, stress corrosion cracking is prevented by performing plastic working after welding so as to eliminate a tensile stress remaining on the storage canister 102 and generate a compressive residual stress (See Non Patent Literature 1). In this technique, for example, the cover is welded to the body of the storage canister 102 and then an operation is performed to apply a compressive stress to and near a welded part. More specifically, nuclear fuel is supplied into the body of the storage canister 102 in a nuclear power plant, a primary cover is welded, and then a secondary cover is welded to seal the nuclear fuel. A tensile residual stress is generated by welding on the top and covers of the body of the storage canister 102 that contains the nuclear fuel. The welded part undergoes plastic working in which a compressive stress is applied by, for example, peening. This eliminates the tensile residual stress and leaves the compressive stress over the outer surface of the storage canister 102. In domestic storage of nuclear fuel, the state of the storage canister 102 is a required condition for preventing stress corrosion cracking.
The sealed storage canister 102 that contains nuclear fuel does not leak a radioactive material to the outside but allows external leakage of radiation through the thin body of the storage canister 102. In order to prevent stress corrosion cracking of the storage canister 102, plastic working needs to be performed so as to face the storage canister 102, leading to an adverse effect of radiation leaking from the storage canister 102.